Biological responses and gene expression differences in two populations of pigs to infection with porcine reproductive and respiratory syndrome virus.

摘要

One hundred pigs from the NE Index Line (I) and 100 Hampshire-Duroc cross pigs (HD) were inoculated intra-nasally with Porcine Respiratory and Reproductive Syndrome virus (PRRSV 97-7895 strain) at 26 d of age to determine whether genetic variation in response to PRRSV exists. An uninfected littermate to each infected pig served as controls. Body weights and rectal temperatures were recorded and blood samples were drawn from each pig at d0 before inoculation and on d4, d7, and d14 post-inoculation. Pigs were sacrificed on d14. Data were analyzed with a mixed model. The interaction of line by treatment was significant (P 0.0001) for weight change and rectal temperature. Uninfected HD pigs gained more weight from d0 to d14 and averaged higher temperature than uninfected I pigs (P 0.0001); whereas infected I pigs gained more weight and had lower temperature than infected HD pigs (P 0.0001). Viremic titer (V) (CCID50/ml) was greater (P 0.05) in HD than I at d4, d7, and d14. Viral titer loads in lung and bronchial lymph nodes did not differ between HD and I pigs. Mean sample to positive (S/P) ratio for infected pigs was higher in HD than in I (P = 0.0009). The HD pigs had greater incidence of interstitial pneumonia and higher lesion scores than I pigs. Principal component analyses were used to rank pigs for phenotypic response to PRRSV. cDNA expression of 12 specific immune markers was evaluated in 7 pigs within each population classed as low (L) responders (high WTDelta, low V, and few lung lesions), and high (H) responders (low WTDelta, high V, and many lesions) in a 2*2*2 factorial treatment design. Significant over-expression in lungs of L pigs relative to controls for certain genes, and of H pigs relative to controls for these same genes, was detected, whereas both over and under-expression of genes in BLN occurred. Serum levels of the immune cytokines confirmed these differences.